Free piston engine



` June 24,r 195s figg;

FREE PISTON ENGINE Filed May 14, 195e w. H. SMITH 2,839,911

z/ 1/ 5L( l' 6./

5 i; fz

v N.0. Z 5f /v Snr/vf@ INVENTOR United States Patent o 2,839,911 FREE PIsToNENGmE Warren H. Smith, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application May 14, 1956, Serial No. 584,744 9 Claims. (c1. 60-97) the engines, "they are ordinarily interconnected 'so that they tend to 'run in phase. This inventionis directed to a system including fan yautomatic vvalve tov break the connection between the'two engines employedV for starting as soon as the engines have started so 'that they vmaybe Vrunout of phase. y,

A principal 'object ofthe y*invention is to provide an improved free` piston gas'pgeneiator o r compressor and to provide animproved starting and'pdephasing system for suchengines. The nature of the invention and the advantages thereofwill he apparent't'o thoseV skilled in the art from the succeeding,detailed/description of the preferred embodiments ofthe inventionand the accompanying'drawings inwhich;

Fig. 1 is a lschematic diagramY of a` dual unit free piston Ygas generator with a `control system embodying the invention; v

,V1-iig. 2 is lapartial, schematic diagram illustrating a modification of the system; Y

Fig. 3 is a schematicr drawing of a pressure operated valve suitable foruse inthe system,and ,Y l

Fig. 4V is a cross sectional View yof the valve taken on the plane indicated yin Fig. 3. Y Y

Referring rst to Fig. l, the` gas generator G includes two units U and U each of which isjfa complete free piston gas generatorof known type, 'each including a power cylinder 1 having'intake ports '2 andexhaust ports 3. Within the cylinder are mounted opposed power pistons 4 which are integral with the compressor pistons 5. The compressor pistons reciprocateiin cylinders 6, the outer ends of lwhich ,define reboundjchambers 6a and the `inner ends of which `delne1compressor cylinders 6b. The' compressor pistonsinspire air through `inlet'valve 7 during the outwardstroke and discharge it through outlet rvalves 8 on the inward stroke into an air boxj9 fwhichcornmunicates with the power cylinder intake ports 2, The exhaustports v3 are connected to 'a common gas discharge'conduitllrby which 't'hefengine exhaust may be conducted toa turbine v(notqshcfiwn).

The lair box-9 is `preferably j common to both Vfree invention is applicable to engines'havingentirely separate air boxes. The common air box for the two units is desirable to'promotegrleater `eiiciency and simplicity of y vstructure in ajdual unit gas generator.,

The two piston assemblies of each unit areconnected .shown in Fig. l.

fs. by linkage (not shown) to insure that they move in synchronism, as is commonly understood. However, the two units are mechanically independent. Since the engine structure is well known to those skilled in the art, it need not be described in detail. l

The frequency of oscillation of the pistons is determined principally by the air pressure in the rebound chambers 6a. This pressure is controlled primarily bya stabilizer S which may be of known type, such as those shown in U. S. Patent No. 2,355,924. The stabilizer is connected to the air box 9 by a conduit 21 and is connected to the cushion chambers 6a of the unit U by a conduit 22 which serves to equalize the pressures in the two rebound chambers of the unit. The stabilizer acts to pass compressed air from the air box to the rebound chambers or vice versa to maintain proper unit operating conditions.

In order to operate the units in the desired out of phase relation Aso that the pistons of one unit are approximately at the inner'dead center when the pistons of the other unit are at outer dead center, the system includes a dephaser 23 which may be Vof any suitable type, such as those, described in U. S. Patent No. 2,473,204. The dephaser acts toV vary slightly the operating speed of one unit relative to the other until the units are out of phase, and thereafter maintain them in such out of phase relation, by bleeding air from the rebound chambers'of one unit to the other. Since the dephaser is explained in the patent referred to and the details are immaterial to this invention, it will'not be described herein. -Various arrangements for Ystarting free piston engines are known in theart. In general, they all involve moving the pistons to an outward position and then impelling them inwardly to compress the air in the power cylinder and cause injection of fuel, thereby putting the engine in operation. Among the preferred starting systems are those which hold the pistons in the outward position until a suitablev starting pressure has been created in the rebound chambers by supplying compressed air thereto, whereupon the holding device is released to allow the pistons to move inwardly. Another preferred starting system involves storing the requisite amount of air for starting in yan accumulator which is rapidly discharged into the rebound chambersto start the engine. The present invention is illustrated as applied to starting systems of both these types, although it will be understood that it may be incorporated in other known starting systems.

While it has been proposed to start dual gas generators out of phase, it is considerably more convenient and practicable to start them simultaneously in phase and subsequently dephase the units..

Fig. l shows a starting system of the latching type for simultaneous starting lof the units. lThis system may include any suitable latching or restraining devices for the pistons. For purposes of illustration, a latching device such as is shown and described in Patent No. 2,473,204 is On the outer end of one compressor piston of each unit there is provided a latch dog 24 fixed to the piston. These latch dogs may be engaged by pivotcd latches 26 after the pistons have been moved to an outward position. Latches 26 are xed on shafts 2.7 exn tending through. the heads of cylinders 6. Arms 2S are iixed on the outer end of these shafts. Latches 26 are normally held out .of engagement with latch dogs Z4 by tension springs Z9 coupled between the latches and the wall of cylinders 6 so. that they do not interfere with the reciprocation of the pistons in normal operation of the engine. For starting'the engine, the latches are Vmoved into engagement with the dogs by piston rods 31 V integral with pistons 32 mounted in iixed cylinders V33.

Theser pistons are actuated 'to activate the latches by'air pressure supplied from the'starting system, as will be described. The means for maneuvering the pistons to the outward position may be of any suitable type and is not described.

Proceeding to the means for charging the cushion chambers with air for starting, this may comprise a compressed air cylinder 34 charged from any suitable source and connected through a line 36, pressure regulating valve 37, and line 38 to a starting control valve 39. Starting control valve is of conventional type including a fixed casing 41 and a valve plug 42 rotatable by a handle 43. By rotating the valve plug 90 from the position shown in the figure, air line38 is connected through conduit 44, check valve 46, and lines 47 and 22 to the rebound chambers of unit U. A line 48 branching from line 47 is connected through normally open valve 50, line 51, and line 22 to the rebound chambers of unit U. Check valve 46 permits flow only from the starting valve 41 to the rebound chambers and preferably is slightly loaded so as to provide a slight pressure drop in the direction in which ow is permitted. v

The latch operating cylindersv 33 are connected through a line 52 to the charging conduit 44 ahead of the check valvel 46. As will be apparent, when the starting valve 39 is shifted to supply air from the regulating valve to line 44, compressed air will be supplied through line 52to cylinders 33 to engage the latches. Air also will flow through valve 46 and the lines previously described to the rebound chambers until the pressure in these chambers has reached a value established by the setting of regulating valve 37.' `In View of the slight'pressure drop across valve 46, the latches will engage before there is any pressure inv the rebound chambers. When the rebound chambers have been charged, the valve 39 is shifted to the position shown in Fig. 1, thereby releasing the pressure in the latch cylinders'33 and releasing the by expansible chamber motor 54 supplied through liney V56 from the air box of the engine in the same manner as shown in Fig. 1. In the system of Fig. 2, it is desirable to provide the symmetrical arrangement of valve 65 and conduits 66 so that the rebound chambers of both engines will receive the same charge when the air bottle of starter 60 is vented into the engine units.

A suitable structure for valve 65 is illustrated somewhat schematically in Figs. 3 and 4. The valve 65 and expansible chamber motor 54 are incorporated ina unitary structure including a casing 71 deining a valve body within which is reciprocably mounted valve spool 72. The valve spool includes lands 73 and 74 engaging the walls of cylinder 76 in the valve body, the lands being provided with suitable seals such as O-rings or piston rings'77 and 78. The lands 73 and 74 are joined by a reduced section stem 79. In theV open position of the valve illustrated in Fig. 3, the ports 81 inthe wall of the cylinder which communicate with lines 61 and 66 are in communicationk through the spacebetween the lands 73 and 74. If the valve moves downwardly, land 73 closes the ports 81, thereby isolating the lines 66 from each other and also from the line 61. It is not necessary that line 61 be isolated,`but this structure provides a symmetrical flow path from line 61 to both of lines 66.

l Valve cylinder 76 may be closed by a head 82 provided with a small vent Yopening 83. Valve spool 72 may be actuated by a stem 84 Asuitably connected to the valve fio each other, thus disabling the dephaser which operates Y' by controlling a slight low of air from the rebound chambers of one unit to the other. Valve is automatically closed as soon as the engine goes Vinto operation. This is preferably accomplished by providing an expansible chamber motor 54 which is actuated by pressure in the air box supplied to the motor through' a line 56. With this arrangement, as soon as the engine is in operation, the compressor cylinders charge the air box and pressure supplied from the air box to motor 54 automatically i closes valve 50, thus isolating the rebound chambers of the two units and permitting-the dephaser 23 to operate.

Fig. 2 illustrates the application of the invention to a startingsys'tem of the type in which the rebound chambers are supplied with air from a system in which an air bottle is charged to a suitable pressure and then quickly discharged into the rebound chambers. Such starting systems are well known, and therefore the means for supplying the metered charge of air is indicated in Fig. 2 simply by the starter and the details thereof, which are immaterial, will not be described. One such starter is described in U; S. Patent No. 2,462,745. In the systemof Fig. 2, the pistons are not provided with latches; they are maneuvered outward to the desired starting position and remain at rest there until the starting air is discharged into the rebound chambers. The starter 60 is connected through a conduit 61 to a normally open valve which is connected through lines 66 and 22 to the rebound chambers of the, units. Valve 65 differs from valve 50 in having three ports, all of which are connected when the valve is opened and all of which are isolated when the valve is closed. Valve 65 maybe closed spool. Stem 84 extends into expansible chamber motor `54 of the diaphragm type, the chamber 85 of which is deiined by a tiange 86 of the valve body and by a cover 87 fixed thereto.Y An enlarged head 88 on stem 84 engages a flexible ydiaphragm 89, the margins of which are clampedv between the edges of flange 86 and cover 87. Control line 56 enters the upper endof the expansible chamber motor through'a boss 91 in the cover 87. A coil compression spring 92 mounted between head 88 and the valve body normally holds the valve in the open position but, whenpressure is transmitted to the upper side of the diaphragm through line 56, thediaphragm forces stem 84 downwardly to close the valve. An atmospheric bleed passage 93 is provided from the upper end of cylinder 76 and likewise a bleed or vent 94 from vthe lower part of motor chamber 85. As will be apparent,vmany suitable valve structures for the purpose may be devised. The foregoing is merely illustrative of a suitable structure. y p

As will be apparent, the valve'50 and valve actuator 54 of the system of'Fig. 1 may be the same as in Figs. 3 and 4, except that only two ports 81 need be provided to communicate with lines 48 and 51. j

It will be apparent also that the motor S4 may respond toV pressures "other than `air box pressures indicative of the fact that the power units have gone into operation, and actuationby means 4responsive to other phenomena is also feasible. AnyY phenomenon conditional upon op eration of the engine may be sensed and used to actuate p suitable mechanism to close valve 50 or 65. However, the use of air box pressure for the purposes is believed to provide the most satisfactory arrangement.

As will be apparent, the invention provides a simple, reliable, and automatic means to convert the engine from operation in unison most suitable for starting to the out of phase mode of operation.

The detailed description of the preferred embodiments of the invention for the purpose of explaining the principles thereof is notto be regarded as limiting or restricting the invention, asY many moditications may be made by the exercise of skill in the art without parting from the principles thereof.

I claim: p Y

1. A free piston power plantfcomprising, in combination, two free piston units each including cylinder and piston means detning a power cylinder, an air compressor, and a rebound chamber, a conduit connecting the rebound chambers of the units, a starter including means for supplying air connected to the said conduit, the starter being adapted to supply air to the rebound chambers to start the units, a normally open valve in the conduit operative to close the conduit between the two units when closed, and means responsive to a condition indicative of operation of the units connected to the valve to close the valve.

2. A free piston power plant comprising, in combination, two free piston units each including cylinder and piston means defining a power cylinder, an air compressor,l and a rebound chamber, means to establish dephased operation of the units, a conduit connecting the rebound chambers of the units, a starter adapted to supply air to the rebound chambers to start the units, a normally open valve in the conduit operative to close the conduit between the two units when closed, and means responsive to a condition indicative of completion of the starting operation connected to the valve to close the valve.

3. A free piston power plant comprising, in combination, two free piston units each including cylinder and piston means dening a power cylinder, an air compressor, a rebound chamber, and means dening an air box connected to the compressor to receive aii discharged therefrom and connected to the power cylinder to supply air thereto, a conduit connecting the rebound chambers of the units, a normally open valve in the conduit operative to close the conduit between the two units when closed, and means responsive to air box pressure connected to the valve to close the valve.

4. A free piston power plant comprising, in combination, two free piston units each including cylinder and piston means defining a power cylinder, an air compressor, a rebound chamber, and means delining an air` box connected to the compressor to receive air discharged therefrom and connected to the power cylinder to supply air thereto, a conduit connecting the rebound chambers of the units, a starter including means for supplying 6 air connected to the said conduit, the starter being adapted to supply air to the rebound chambers to start the units, a normally open valve in the conduit operative to close the conduit between the two units when closed, and means responsive to air boX pressure connected to the valve to close the valve.

5. A free piston power plant comprising, in combination, two free piston units each including cylinder and piston means defining a power cylinder, an air compressor, a rebound chamber, and means defining an air box connected to the compressor to receive air discharged therefrom and connected to the power cylinder to supply air thereto, a dephaser connected to the rebound chambers of both units adapted to bleed air between the rebound chambers to establish dephased operation of the units, a conduit connecting the rebound chambers of the units, a starter including means for supplying air connected to the said conduit, the starter being adapted to supply air to the rebound chambers to start the units, a normally open valve in the conduit operative to close the conduit between the two units when closed, and means responsive to air box pressure connected to the valve to close the valve.

6. A power plant as recited in claim 4 including means for holding the piston means in starting position and means connected to the holding means and the starter operative to release the holding means.

7. A power plant is recited in claim 4 in which the normally open valve has three ports closed by the valve when the valve is closed, two of the ports being connected in the conduit and the third port connecting the conduit to the starter.

8. A power plant as recited in claim 1 in which the last-recited means is responsive to a pressure developed by a unit during operation thereof.

9. A power plant as recited in claim 2 in which the last-recited means is responsive to a pressure developed by a unit during operation thereof.

No references cited. 

